Acute Myeloid Leukemia With NPM1 Mutation Presenting With Rapidly Progressing Hypereosinophilia.

Hypereosinophilia presents a significant clinical challenge. We describe a case of severe, rapidly progressing hypereosinophilia, with the white blood cell count increasing from 40,000/μL to over 130,000/μL within days, and 70% eosinophils on differential count. The patient initially presented with diffuse symptoms but developed eosinophilic myocarditis during hospitalization. Targeted next-generation sequencing identified a mutation in NPM1 and according to the WHO 5^th edition criteria, the patient was diagnosed with acute myeloid leukemia (AML) with NPM1 mutation. Whole genome and transcriptome sequencing revealed a concurrent fusion ETV6::ACSL6. This fusion has been previously described in myeloid diseases with eosinophilia. Despite initial deep response to AML treatment, reaching MRD-negativity for NPM1, the patient relapsed shortly after stem cell transplantation and died.